Discharge-Bypass Valves Installation

Bypass valves can be installed in horizontal or vertical lines, whichever best suits the application and permits easy accessibility to the valves. However, consideration should be given to locating these valves so that they do not act as oil traps. Also solder must not run into the internal parts during brazing.

The DBV should always be installed at the condensing unit rather than at the evaporator section. This will ensure the rated bypass capacity of the DBV. It will also eliminate the possibility of hot gas condensing in the bypass line. This is especially true on remote systems.

When externally equalized lines are used, the equalizer connection must be connected to the suction line where it will sense the desired operating pressure. See Fig. 11-40.

Since the DBV is applied in a bypass line between the discharge line and the low side of a system, the valve is subjected to compressor vibrations. Unless the valve, connecting fittings, and tubing are properly isolated from the vibrations, fatigue failures may occur. While the heaviest valve weights only 3.5 lb (1.6 kg), it should be adequately supported to prevent excessive stress on the connections..

If the remote-bulb type bypass valve is used, the bulb must be located in a fairly constant ambient temperature because the element-bulb assembly is air charged. These valves are set at the factory in an 80°F (27°C) ambient temperature. Thus, any appreciable variation from this temperature will cause the pressure setting to vary from the factory setting. For a nonadjustable valve, the remote bulb may be located in an ambient 80°F ±10°F (27°C ± 5.5°C) The adjustable remote bulb model can be adjusted to operate in a temperature of 80°F ± 30°F (27°C ± 16.7°C). On many units the manufacturer will have altered the pressure setting to compensate for an ambient temperature appreciably different than 80°F (27°C). Therefore on some units it may be necessary to consult with the equipment manufacturer for the proper opening pressure setting of the bypass valve

There are numerous places on a system where the remote bulb can be located. Two possible locations are the return air stream and a structural member of the unit, if it is located in a conditioned space. Other locations, where the temperature is fairly constant but different than 80°F (27°C) are also available. These include the return water line on a chiller, the compressor suction line, or the main liquid line. As previously mentioned, the setting may have been altered.

A bulb strap with bolts and nuts is usually supplied with each remote bulb-type DBV. This strap is for the use in fastening the bulb in place.

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